Train switches, also known as points, are essential components of railway tracks that allow trains to change from one track to another. They essentially work by physically moving a small section of rail to guide the train wheels onto a different path.
At its core, a train switch consists of a few key parts:
- Stock Rails: These are the two main rails of the track that continue straight.
- Points (Switch Rails): These are a pair of movable rails, tapered at one end (the switch toe) and hinged or pivoted at the other (the switch heel).
- Switch Stand or Actuator: This is the mechanism used to move the points. It can be operated manually with a lever or automatically with electric or hydraulic power.
- Crossing (Frog): This is where the rails intersect, allowing the wheels to pass from one track to another without derailing.
The Switching Mechanism
The process of changing a train's path using a switch is straightforward:
- Actuating the Switch: The operator (or system) initiates the change by operating the switch stand or actuator. When the switch stand lever is thrown, the points move from one running rail to the other.
- Point Movement: One of the pointed rails (the point) is moved tight against its corresponding stock rail, creating a continuous path for the train wheels. Simultaneously, the other point is moved away from its stock rail, creating a gap that prevents the train from entering that path.
- Guiding the Train: As the train approaches, its wheels follow the path created by the points. If the switch is set for the straight track, the wheels stay on the original rails. If it's set for the diverging track, the tapered points guide the wheels onto the new rails, directing the train onto the alternate route.
- Signaling the Position: Switch stands often include visual indicators. As the points move from side to side, a pair of sign plates (called targets) on the switch stand turn 90 degrees. These targets visually show the switch's position to train crews. Traditionally, the targets have consisted of one green plate and one red plate. The visible color indicates which path is set (e.g., green for straight, red for diverging, or vice-versa, depending on the railway's standard).
Visual Indicators: Targets
- Green Target: Often indicates the switch is set for the main or straight track.
- Red Target: Typically indicates the switch is set for the diverging or side track.
These visual cues are crucial for safety, allowing engineers to confirm the switch position from a distance before their train reaches it.
In summary, train switches work by mechanically shifting movable rails (points) to align with different stock rails, creating a new path for the train's wheels, with integrated targets providing a visual signal of the switch's current setting.
